The Shackleton Range occupies a key geological position in Antarctica (Fig. 1). Its location, at the edge of the continental craton between the mobile belts of the Transantarctic Mountains (TAM) and the stable platform of Dronning Maud Land (Neuschwabenland), and its geological constitution offer possibilities for: understanding the nature of the ‘Pacific’ margin of the Antarctic craton during the Palaeozoic, distinguishing between subduction- and collision-related tectonics at an ancient continental margin, and contributing to the debate on the relationship between East and West Antarctica. The structural orientation of the range, at right angles to the trend of the TAM, has puzzled geologists ever since its discovery.

It is hard to divorce most human activities, including science, completely from politics. Politics is about perceived certainty whilst science is about doubt – they make strange bedfellows. Politicians detest probabilities whilst scientists abhor the absolute. Nowhere is the relationship between politics and science more publicly developed than in the Antarctic Treaty System. In the only continent devoted to peace and science it might be supposed that, after more than thirty years, the role of science would be both more robust and more pivotal in decision-making than elsewhere in the world. So it appears at present but will it remain so?

New reference gravity values are provided for gravity base stations at McMurdo Station and Scott Base. The new values are obtained by a relative survey including the Hut Point base station (an International Satellite Triangulation station; 77.8448°S, 166.6418°E; 982975.65 mGal) located 110 m north of Scott’s 1901 Discovery Hut at McMurdo Station. This site is the only remaining station tied by previous surveys to the now defunct SATGRAV base Station located in the former Building 57, which was, in turn, measured by an absolute meter in 1995. New values are 982970.41 mGal for the THIEL-1 Station (77.8490°S, 166.6794°E) at McMurdo Station, 982973.40 mGal for the MMD-N Station (77.8491°S, 166.7567°E) at Scott Base, and 982977.83 mGal for the newly established SBG-1 Station (77.8499°S, 166.7667°E) under the flagpole at Scott Base. Our difference values are very consistent with previous surveys, including Nakagawa’s value for MMD-N at Scott Base, which is within 0.2 mGal of our new value.

We investigate two ice rises, Kupol Moskovskij and Kupol Ciolkovskogo, in the Fimbul Ice Shelf, East Antarctica, situated ~60 km from each other but differing in their glaciological settings. We apply a thermo-mechanically coupled Elmer/Ice model to profiles going across these ice rises and use it to investigate their past evolution covering present to several millennia ago. We constrain the model results using field measurements, including surface-velocity measurements, and surface mass balance estimated by isochronous radar stratigraphy dated with firn cores. We find that the ice rises are thickening at present (2012–2014), which started only in recent decades. Investigation of deeper radar reflectors suggests a stronger upwind-downwind contrast in surface mass balance in the past for both ice rises, with varying details. This result matches what was previously found on Blåskimen Island ice rise, which is also in the Fimbul Ice Shelf. Moreover, Kupol Moskovskij, situated at a shear margin, shows signs of recent changes in its ice-divide position, while Kupol Ciolkovskogo shows a more stable divide position. This study highlights the long-term influence of surface mass balance on ice rises, as well as the strong influence of local glaciological settings on their evolution.

A model to estimate the annual layer thickness of deposited snowfall at a deep ice core site, compacted by vertical strain with respect to depth, is assessed using ultra-high-resolution laboratory analytical techniques. A recently established technique of high-resolution direct chemical analysis of ice using ultra-violet laser ablation inductively-coupled plasma mass spectrometry (LA ICP-MS) has been applied to ice from the Berkner Island ice core, and compared with results from lower resolution techniques conducted on parallel sections of ice. The results from both techniques have been analysed in order to assess the capability of each technique to recover seasonal cycles from deep Antarctic ice. Results do not agree with the annual layer thickness estimates from the age–depth model for individual samples <1 m long as the model cannot reconstruct the natural variability present in annual accumulation. However, when compared with sections >4 m long, the deviation between the modelled and observational layer thicknesses is minimized to within two standard deviations. This confirms that the model is capable of successfully estimating mean annual layer thicknesses around analysed sections. Furthermore, our results confirm that the LA ICP-MS technique can reliably recover seasonal chemical profiles beyond standard analytical resolution.

Antarctica was once considered biologically isolated, surrounded by oceanic barriers (Fraser et al. 2018). However, floating materials such as kelp rafts (Fraser et al. 2018, Avila et al. 2020), wood (Lewis et al. 2005) and plastics (Avila et al. 2020) are now known to cross these barriers and reach Antarctic shores. Such incursions might enable non-native species (either rafting species themselves or associated hitchhikers) to colonize Antarctica as the climate warms (Avila et al. 2020, Fraser et al. 2020), but whether these species will be able to survive and reproduce in the Antarctic is not yet known. Sea ice is a defining characteristic of Antarctic coastlines, and modelled trajectories of kelp rafts (Fraser et al. 2018) cross-referenced against sea-ice observations (Parkinson 2019) suggest that collisions between rafts and seasonal sea ice occur frequently (Fig. 1a); thus, rafts are expected to be entrained in, on or under sea ice and experience multiple freeze-and-thaw cycles on their journeys to Antarctica. In addition, kelp rafts that reach the Antarctic intertidal will experience temperatures well below 0°C if exposed to the air at low tide. Freezing can cause severe disruptive stress to seaweeds, and ice crystals growing in intercellular spaces can damage cell membranes and cause cell lysis (Eggert 2012). Such damage could affect the buoyancy of kelp tissue and decrease rafting ability. Although some non-native kelp rafts recovered from Antarctic shores appeared to still be reproductively viable, with mature gametes observed in reproductive tissue (Fraser et al. 2018), tissue damage caused by freezing could have widespread effects on the health, function and establishment success of a non-native species traversing the Southern Ocean.

Burrow-nesting seabirds constitute an important part of seabird diversity, yet accurate estimates of their abundance are largely lacking, limiting our understanding of their population dynamics and conservation status. We conducted a survey to estimate the number of South Georgia diving petrel (Pelecanoides georgicus) burrows during the 2013–14 breeding season on Ile de la Possession, Crozet archipelago, southern Indian Ocean. We used distance sampling and acoustic playback in order to estimate burrow densities in a priori-selected favourable nesting areas. A total of 855 burrows were detected. The mean altitude of burrows was 601.8 ± 69.4 m. The mean burrow detection distance was 1.77 ± 1.63 m. The burrow density was estimated at 15.649 burrows ha-1 (95% confidence interval (CI): 10.245–23.903) and the slope-corrected total favourable area was 2365.53 ha, which yielded an estimate 37 018 burrows (95% CI: 24 235–56 544). The playback response rate was 15.8 ± 1.3%, and 40.8 ± 1.7% of burrows were occupied or showed signs of occupation. Occupancy rates were low compared to those measured by systematic burrow inspection in other studies. Assuming that laying occurred in 80–93% of the estimated number of burrows, as estimated by previous studies, gives an estimate of 29 614 (95% CI: 19 388–45 235) to 34 426 (95% CI: 22 538–52 585) breeding pairs.